On 8/18/2014 9:09 AM, Jan Včelák wrote: > Hello list, > > we develop an authoritative DNS server called Knot DNS and we use the > userspace-rcu library [1] for synchronization. The library implements the > synchronization by inserting appropriate sfence/lfence/mfcence instructions > and some reference counting around. > > Currently, we are trying to track down an invalid read reported by Valgrind. > The problem appears very rarely and it's quite difficult to reproduce. > Valgrind claims that a previously freed memory is being read. However we quite > sure that the synchronization is correct and that this problem should not > happen. > > Does Valgrind support the mentioned memory barrier instructions?
If it did not *recognize* the instruction, then valgrind would bomb out with an error message giving the op code byte sequence and saying it did not recognize it. A possibility is that it recognizes the instruction but does not implement it as you expect. Someone else will need to answer as to that possibility. > I'm not rejecting that there is a problem in our code, but I want to make sure > that we are chasing a real bug. You might want to verify that valgrind and your code have the same notion of what the malloc/free routines are, etc., i.e., that valgrind is able to hook into all allocation and freeing calls your application uses. Best wishes -- Eliot Moss ------------------------------------------------------------------------------ _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
